The State Department has announced the U.S. is imposing sanctions against three Chinese entities for transferring chemical and biological weapons technology to Iran. The move comes less that a month before President Bush is to visit Beijing for a summit with his Chinese counterpart, Jiang Zemin.

The sanctions decision was announced with little fanfare in a posting in the U.S. government's official daily publication, the Federal Register.

Under its terms, the three Chinese firms will be barred from doing business with the U.S. government or benefiting under the Iran Non-Proliferation Act approved by Congress two years ago.

At a briefing here, State Department spokesman Richard Boucher said the penalties were imposed because of the companies' transfer to Iran of equipment and technology used for the manufacture of chemical and biological weapons.

He said U.S. officials have long been pressing China to bring its control policies into line with those of other major industrial countries. "As you know, we've had a long-standing dialogue with China on non-proliferation issues and, overall, sought to get China to abide by or impose similar standards to those that the rest of the international community follows when it comes to these kinds of transfers," he said.

Mr. Boucher said the affected firms were the China Machinery and Electric Import and Export Company, the Lyang Chemical Equipment Company and a third concern, identified only as Q.C. Chen.

Officials here said it was unclear whether the Chinese government had knowledge of their transactions with Iran, or whether the firms had any dealings with the United States that would be affected by the new sanctions.

It was the second time in less than six months that the Bush administration has moved against Chinese companies allegedly involved in proliferation.

Last September, it imposed sanctions against a state-owned Chinese firm said to have been providing missile technology to Pakistan.

The proliferation issue has been a major point of contention at recent high-level U.S.-Chinese meetings, and it is expected to be on the agenda when President Bush visits the Chinese capital next month.